Diffusion in Multicomponent Metallic Systems: I. Phenomenological Theory for Substitutional Solid Solution Alloys

Onsager's generalization of Fick's law for diffusion in multicomponent systems is examined with a view to determining the conditions imposed on the diffusion coefficients by the second law of thermodynamics and by "microscopic reversibility." The generalized differential equations with constant coefficients, obtained by combining Fick's law and the continuity equations, are solved for the boundary conditions corresponding to the semi-infinite diffusion couple.